Add rust dataloader

Author: pyros2097

README.md

@@ -473,6 +473,8 @@ Looking to get started with a specific back-end? Try the [loaders in the example
   * [dataloader](https://github.com/absinthe-graphql/dataloader)
 * Golang
   * [Dataloader](https://github.com/nicksrandall/dataloader)
+* Rust
+  * [Dataloader](https://github.com/cksac/dataloader-rs)
 
 ## Video Source Code Walkthrough